• Journal of Mechanical Science and Technology
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• v.18 no.12
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• pp.2114-2124
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• 2004

In this paper, a structural damage identification method (SDIM) is developed for cylindrical shells and the numerically simulated damage identification tests are conducted to study the feasibility of the proposed SDIM. The SDIM is derived from the frequency response function solved from the structural dynamic equations of damaged cylindrical shells. A damage distribution function is used to represent the distribution and magnitudes of the local damages within a cylindrical shell. In contrast with most existing modal parameters-based SDIMs which require the modal parameters measured in both intact and damaged states, the present SDIM requires only the FRF-data measured in the damaged state. By virtue of utilizing FRF-data, one is able to make the inverse problem of damage identification well-posed by choosing as many sets of excitation frequency and FRF measurement point as needed to obtain a sufficient number of equations.

• Structural Engineering and Mechanics
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• v.45 no.6
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• pp.779-802
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• 2013

In this paper, adaptive neuro-fuzzy inference system (ANFIS) and artificial neural networks (ANNs) techniques are developed and applied to identify damage in a model steel girder bridge using dynamic parameters. The required data in the form of natural frequencies are obtained from experimental modal analysis. A comparative study is made using the ANNs and ANFIS techniques and results showed that both ANFIS and ANN present good predictions. However the proposed ANFIS architecture using hybrid learning algorithm was found to perform better than the multilayer feedforward ANN which learns using the backpropagation algorithm. This paper also highlights the concept of ANNs and ANFIS followed by the detail presentation of the experimental modal analysis for natural frequencies extraction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.160-166
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• 1997

The spindle motor in a computer hard disk drive can be modeled as a rotor-bearing system supported by the base plate. Ball bearing is the crucial element to determine the stiffness of the spindle motor, and its design parameters and operating conditions determine the dynamic characteristics of the spindle motor. In the analysis of a rotor-bearing system with a short shaft like a spindle motor, the stiffness of the base plate as well as ball bearings must be considered accurately to analyze the dynamic charateristics of a spindle motor. In this paper, the lateral and the axial vibration of the spindle motor were analyzed by the transfer matrix method for the dual-shaft rotor-bearing model and by d.o.f lumped parameter model, respectively. The simulation results had good agreements with the experimental modal testing. The dynamic characteristics were fully investigated for the change of the major design parameters of the spindle motor, i.e. the preload of ball bearings and the rotational speed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.420-423
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• 2003

This paper addresses the results of experimental and analytical study on the effects of dynamic interaction between vehicle and bridge on modal properties of bridge. Based on ambient vibration test and vehicle impact test on a bridge, it is found that the natural frequencies of bridge are varied by vehicle passing. Analytical studies for the effects of vehicle position, speed, damping, mass ratio and frequency ratio on bridge-vehicle interaction are carried out using complex eigenvalue analysis and numerical integration in time domain. The results show that vehicle properties except speed cause significant change of natural frequency as well as damping of bridge.

• Smart Structures and Systems
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• v.29 no.3
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• pp.387-393
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• 2022

This paper presents the vibration analysis of cracked ceramic-reinforced aluminum composite beams by using a method based on changes in modal strain energy. The crack is considered to be straight. The effective properties of composite materials of the beams are estimated through Mori-Tanaka micromechanical model. Comparison study and numerical simulations with various parameters; ceramic volume fraction, reinforcement aspect ratio, ratio of the reinforcement Young's modulus to the matrix Young's modulus and ratio of the reinforcement density to the matrix density are taken into investigation. Results demonstrate the pronounced effects of these parameters on intact and cracked ceramic aluminum beams.

• Smart Structures and Systems
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• v.4 no.2
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• pp.195-208
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• 2008

This paper summarizes the experimental vibration-based structural health monitoring study on a historical monument in Jordan. In this work, and within the framework of the European Commission funded project "wide-Range Non-Intrusive Devices Toward Conservation of Historical Monuments in the Mediterranean Area", a seven and a half century old minaret located in Ajloun (73 km north of the capital Amman) is studied. Because of their cultural value, touristic importance and the desire to preserve them for the future, only non-destructive tests were allowed for the experimental investigation of such heritage structures. Therefore, after dimensional measurements and determination of the current state of damage in the selected monument, ambient vibration tests are conducted to measure the accelerations at strategic locations of the system. Output-only modal identification technique is applied to extract the modal parameters such as natural frequencies and mode shapes. A Non-linear version of SAP 2000 computer program is used to develop a three-dimensional finite element model of the minaret. The developed numerical model is then updated according to the modal parameters obtained experimentally by the ambient-vibration test-results and the measured characteristics of old stone and deteriorated mortar. Moreover, a parametric identification method using the N4Sid state space model is employed to model the dynamic behavior of the minaret and to build up a robust, immune and noise tolerant model.

• Nuclear Engineering and Technology
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• v.30 no.5
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• pp.416-423
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• 1998

Many studies for the perforated plates have been done, especially on the subject of static behavior and stress distribution in the plate. Equivalent elastic properties are one of the successive concepts for this problem. However little effort was taken to get their dynamic characteristics. In this paper finite element modal analysis was performed for the perforated plates having square and triangular hole patterns. An attempt to use existing equivalent elastic properties into the modal analysis of the plate was carried out. To verify feasibility of the finite element models, modal test was also performed on one typical perforated plate. System parameters such as natural frequencies and mode shapes were extracted and compared with the analysis results.

• Journal of KSNVE
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• v.9 no.1
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• pp.60-69
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• 1999

In the first paper of this research$^{(1)}$. a new time series method. directional ARMAX (dARMAX) model-based approach. was proposed for rotordynamics identification. The dARMAX processes complex-valued signals, utilizing the complex modal testing theory which enables the separation of the backward and forward modes in the two-sided frequency domain and makes effective modal parameter identification possible. to account for the dynamic characteristics inherent in rotating machinery. In this second part. an evaluation of its performance characteristics based on both simulated and experimental data is presented. Numerical simulations are carried out to show that the method. a complex time series method. successfully implements the complex modal testing in the time domain. and it is superior in nature to the conventional ARMAX and the frequency-domain methods in the estimation of the modal parameters for isotropic and weakly anisotropic rotor systems. Experiments are carried out to demonstrate the applicability and the effectiveness of the dARMAX model-based approach, following the proposed fitting strategy. for the rotordynamics identification.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.421-432
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• 2002

In this study the modal characteristics and responses of an asymmetric structure with added viscoelastic dampers were investigated for design parameters such as eccentricity of stiffness and added dampers, the loss factor of the damping materials used. For modal characteristics, variation of the quantities such as natural frequencies, modal damping ratios, modal participation factors, and dynamic amplification factors were observed, and displacements at flexible and stiff edges, and at center of mass were obtained. Based on the results, the problem of the optimum damper distribution to minimize the torsional effects was addressed, and the proposed method for optimum damper distribution was applied to a multi-story structure to verify the applicability Finally the effect of viscous and viscoelastic dampers were compared by varying the loss factor of the viscoelastic material.

• Smart Structures and Systems
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• v.17 no.3
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• pp.431-444
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• 2016

This paper was written in the context of a benchmark study promoted by The Hong Kong Polytechnic University using data samples collected in an instrumented cable-stayed bridge. The main goal of the benchmark test was to study the identification of the bridge modes of vibration under different wind conditions. In this contribution, the tools developed at ViBest/FEUP for automated data processing of setups collected by dynamic monitoring systems are presented and applied to the data made available in the context of the benchmark study. The applied tools are based on parametric output only modal identification methods combined with clustering algorithms. The obtained results demonstrate that the proposed algorithms succeeded to automatically identify the modes with relevant contribution for the bridge response under different wind conditions.